Hundreds of angry people gathered at the scene, blaming the armed militias that hold sway on the streets, and calling for them to be driven from Benghazi, cradle of the uprising that ended Muammar Gaddafi's dictatorship in 2011.
"This is the flesh of our sons, this is what the militias have given us," said a witness at the scene. "All we need here are the police and the army."
The blast damaged a dozen or more vehicles and shattered the windows of buildings nearby, sending up a thick cloud of smoke and flinging dust and debris several blocks.
"This attack is not an isolated incident, but part of a series of incidents targeting the Libyan nation," Prime Minister Ali Zeidan told a news conference in Tripoli.
On Sunday night, the police in Benghazi, Libya's second city, were bombed for the third time in four days.
And in a further sign of the power wielded by the militias that formed to fight Gaddafi and have yet to disarm, gunmen besieged the foreign and justice ministries in Tripoli for two weeks to force parliament to pass a sweeping law barring anyone who held senior office under Gaddafi from serving in government.
Libya's parliament cancelled a session on Monday to allow members from Benghazi to return home and attend the funerals of those killed in the latest attack, for which no one claimed responsibility.
One doctor said three deaths were confirmed in Monday's blast, including a child, and that 17 people were wounded. Another said the fact that the victims had been blown to pieces made it hard to be sure how many had died.
